Venous Stasis Disease (VSD), characterized by edema, occurs when there is an obstruction and/or incompetence of the venous valves or veins in the arms and legs. Edema, an atypical accumulation of fluid in the interstitial space, is caused by fluid leaking out of the vasculature into the surrounding tissue subsequent to the buildup of pressure in the venous walls. While uncomfortable for the patient and capable of leading to other serious complications, edema can be an indicator of the extent of VSD.
One of the complications resulting from VSD are leg ulcers. If the valves are damaged the blood can backflow causing high pressure in the veins. Under these conditions fluids that are normally retained in the veins leak out, resulting in swelling in the legs. This swelling can prevent oxygen, which is carried in the blood and necessary for the healing process, from reaching the wound site. Compression therapy is often used as treatment with the rationale that if the excess fluid can be squeezed out, oxygen can return and the wound can heal.
Currently, there is no device which is capable of measuring the severity of edema in a feasible, economical and quantifiable way. The most widely used clinical method for assessing the amount of edema is digital manipulation. This assessment is accomplished by pressing into the patient's leg and qualitatively evaluating the degree of pitting. Pitting is the indentation in the swollen tissue that remains following removal of pressure from the edemous area. Due to the altered tissue composition resulting from edema, there is a putty-like consistency to the tissue, and the tissue remains in the indented position for seconds to minutes before returning to its original form. The doctor performing the test assesses the depth of the indention, how much force is required to reach the tibia, for example, how long the tissue takes to return to the original state, and skin quality. The level of edema is described using a ranking system of one to four (slight to severe). Despite the qualitative nature of this technique, it is still considered the state of the art for edema assessment. There is a continuing need to improve the assessment of edema that is reliable and economical.